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authorDon Zickus <dzickus@redhat.com>2011-04-27 06:32:33 -0400
committerIngo Molnar <mingo@elte.hu>2011-04-27 17:59:11 +0200
commit2bce5daca28346f19c190dbdb5542c9fe3e8c6e6 (patch)
tree01543a887959d5e5d821c3ce77c171d96eac78fe
parent6c8a7213278324f381cbcbf51510711ed745d8e6 (diff)
downloadop-kernel-dev-2bce5daca28346f19c190dbdb5542c9fe3e8c6e6.zip
op-kernel-dev-2bce5daca28346f19c190dbdb5542c9fe3e8c6e6.tar.gz
perf, x86, nmi: Move LVT un-masking into irq handlers
It was noticed that P4 machines were generating double NMIs for each perf event. These extra NMIs lead to 'Dazed and confused' messages on the screen. I tracked this down to a P4 quirk that said the overflow bit had to be cleared before re-enabling the apic LVT mask. My first attempt was to move the un-masking inside the perf nmi handler from before the chipset NMI handler to after. This broke Nehalem boxes that seem to like the unmasking before the counters themselves are re-enabled. In order to keep this change simple for 2.6.39, I decided to just simply move the apic LVT un-masking to the beginning of all the chipset NMI handlers, with the exception of Pentium4's to fix the double NMI issue. Later on we can move the un-masking to later in the handlers to save a number of 'extra' NMIs on those particular chipsets. I tested this change on a P4 machine, an AMD machine, a Nehalem box, and a core2quad box. 'perf top' worked correctly along with various other small 'perf record' runs. Anything high stress breaks all the machines but that is a different problem. Thanks to various people for testing different versions of this patch. Reported-and-tested-by: Shaun Ruffell <sruffell@digium.com> Signed-off-by: Don Zickus <dzickus@redhat.com> Cc: Cyrill Gorcunov <gorcunov@gmail.com> Link: http://lkml.kernel.org/r/1303900353-10242-1-git-send-email-dzickus@redhat.com Signed-off-by: Ingo Molnar <mingo@elte.hu> CC: Cyrill Gorcunov <gorcunov@gmail.com>
-rw-r--r--arch/x86/kernel/cpu/perf_event.c12
-rw-r--r--arch/x86/kernel/cpu/perf_event_intel.c10
-rw-r--r--arch/x86/kernel/cpu/perf_event_p4.c17
3 files changed, 33 insertions, 6 deletions
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index fac0654..e638689 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1288,6 +1288,16 @@ static int x86_pmu_handle_irq(struct pt_regs *regs)
cpuc = &__get_cpu_var(cpu_hw_events);
+ /*
+ * Some chipsets need to unmask the LVTPC in a particular spot
+ * inside the nmi handler. As a result, the unmasking was pushed
+ * into all the nmi handlers.
+ *
+ * This generic handler doesn't seem to have any issues where the
+ * unmasking occurs so it was left at the top.
+ */
+ apic_write(APIC_LVTPC, APIC_DM_NMI);
+
for (idx = 0; idx < x86_pmu.num_counters; idx++) {
if (!test_bit(idx, cpuc->active_mask)) {
/*
@@ -1374,8 +1384,6 @@ perf_event_nmi_handler(struct notifier_block *self,
return NOTIFY_DONE;
}
- apic_write(APIC_LVTPC, APIC_DM_NMI);
-
handled = x86_pmu.handle_irq(args->regs);
if (!handled)
return NOTIFY_DONE;
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 9ae4a2a..e61539b 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -933,6 +933,16 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
cpuc = &__get_cpu_var(cpu_hw_events);
+ /*
+ * Some chipsets need to unmask the LVTPC in a particular spot
+ * inside the nmi handler. As a result, the unmasking was pushed
+ * into all the nmi handlers.
+ *
+ * This handler doesn't seem to have any issues with the unmasking
+ * so it was left at the top.
+ */
+ apic_write(APIC_LVTPC, APIC_DM_NMI);
+
intel_pmu_disable_all();
handled = intel_pmu_drain_bts_buffer();
status = intel_pmu_get_status();
diff --git a/arch/x86/kernel/cpu/perf_event_p4.c b/arch/x86/kernel/cpu/perf_event_p4.c
index d1f77e2..e93fcd5 100644
--- a/arch/x86/kernel/cpu/perf_event_p4.c
+++ b/arch/x86/kernel/cpu/perf_event_p4.c
@@ -950,11 +950,20 @@ static int p4_pmu_handle_irq(struct pt_regs *regs)
x86_pmu_stop(event, 0);
}
- if (handled) {
- /* p4 quirk: unmask it again */
- apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED);
+ if (handled)
inc_irq_stat(apic_perf_irqs);
- }
+
+ /*
+ * When dealing with the unmasking of the LVTPC on P4 perf hw, it has
+ * been observed that the OVF bit flag has to be cleared first _before_
+ * the LVTPC can be unmasked.
+ *
+ * The reason is the NMI line will continue to be asserted while the OVF
+ * bit is set. This causes a second NMI to generate if the LVTPC is
+ * unmasked before the OVF bit is cleared, leading to unknown NMI
+ * messages.
+ */
+ apic_write(APIC_LVTPC, APIC_DM_NMI);
return handled;
}
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